1. Field of the Disclosure
The present disclosure relates to a method, a system and a device for generating power from the kinetic energy of a fluid current. More particularly, the disclosure relates to a method, a system and a device for controlling, modulating and maximizing a power output from a hydrokinetic device, including an array of hydrokinetic devices.
2. Related Art
Kinetic energy of flowing ocean currents represents a significant source of clean renewable energy. The water that comprises the world's oceans is constantly in motion, and in many locations there exist repeatable, consistent and rapidly moving ocean currents with speeds in excess of 1.0 meters-per-second (m/s). Examples of ocean currents include the Gulf Stream, the Humboldt, the Kuroshio, the Agulhas and others. These currents have their origins in ocean thermal and salinity gradients, Coriolis forces, and other ocean thermal transport mechanisms.
These currents represent “rivers in the ocean” which lie predominantly in continental shelf areas with bottom depths in excess of 300 meters. Such depths necessitate mooring a hydrokinetic device with cables or tethers to upstream anchors fixed to the sea bed. These ocean currents tend to exhibit an inverse velocity shear profile. Namely, the current velocity decreases in speed as one travels deeper in a near linear relationship. This free stream current flow behavior provides an opportunity to control, modulate and maximize energy output by actively positioning the hydrokinetic device at the operating depth at which the rated speed occurs, thereby facilitating rated power to be output by the attached electrical generator.
Current hydrokinetic devices are typically deployed at a particular depth and maintained at that depth, with variable speed adjustments. U.S. Pat. No. 6,091,161 appears to disclose a method for controlling an operating depth of a tethered water current driven turbine device. The device is kept midway between a prescribed maximum depth and a prescribed minimum depth, and preferably at a midpoint between the two prescribed depths. As a consequence of using a constant depth approach, the device must operate at whatever free stream current speeds occur in the specified depth range, including speeds above a rated speed of the turbine, where power shedding and relinquishment is required, or speeds below a rated speed, where the generator is only capable of outputting partial power. The patent appears to disclose, for example, that in response to an increased current speed, the device would increase buoyancy and/or hydrodynamic lift to remain at the same depth, thereby avoiding from being pulled to deeper depths.
U.S. Pat. No. 7,291,936 appears to disclose a fully submersible electrical power generating plant device. The disclosed device appears to employ a constant depth, variable speed method analogous to that disclosed in U.S. Pat. No. 6,091,161. The method disclosed in the '936 patent appears to require, in response to increasing current speeds, increasing hydrodynamic lift of the device by pitching the entire device and an attached hydroplane wing to a larger angle of attack, thereby creating greater hydrodynamic lift to kept the device at the same depth and avoid from being pulled deeper.
The present disclosure provides a hydrokinetic device that harnesses the kinetic energy of flowing water currents to provide clean, renewable energy, as well as a method, a system and a device for providing substantially constant speed and variable depth adjustment of the hydrokinetic device to maximize and/or modulate power generation.